There has been heretofore known a power supply device in which electrical charges are stored in a plurality of capacitors to use these charges as electrical power for electronic equipment and the like. In such a power supply device, the fluctuation of output voltage due to a variation in a state-of-charge of the capacitors becomes a problem. In order to obtain a constant output voltage even if the state-of-charge of the capacitors varies, it is conceivable to use, for example, a switching power supply, such as a heretofore-known DC-DC converter or the like. Incorporating a switching power supply causes electrical power loss, however, and may cause a significant increase in the size and cost of the power supply device.
Hence, as a related art intended to prevent output voltage fluctuations due to a variation in the state-of-charge of capacitors without incorporating any switching power supplies, there has been heretofore known a power supply device in which a bypass circuit is provided in each of capacitors to switch the connection of the capacitors according to the state-of-charge of each capacitor (see, for example, Patent Document 1). There has also been heretofore known a power supply device in which for the same purpose as described above, a plurality of intermediate tap output terminals for extracting electrical power from each connection point of capacitors through a switch is disposed to control each switch according to the voltage fluctuation of the capacitors, thereby switching among the intermediate tap output terminals (see, for example, Patent Document 2).
In a power supply device configured in such a way as described above, there arises the problem of the state-of-charge of capacitors becoming imbalanced for reasons of the configuration. As a related art intended to solve such a problem, there has been heretofore known a power supply device in which, for example, a plurality of taps for extracting electrical power from each connection point of capacitors through a switch is disposed to select a capacitor to be connected to a battery charger through these taps according to the voltage of the battery charger at the time of charging (see, for example, Patent Document 3). There has also been heretofore known a power supply device in which for the same purpose as described above, a plurality of output capacitors and a plurality of adjusting capacitors are disposed, the adjusting capacitors are series-connected to or disconnected from the output capacitors to adjust an output voltage, and relaxation charging is performed on adjusting capacitors not connected to any output capacitors, in order to prevent voltage reduction due to self-discharge (see, for example, Patent Document 4).